1. Field of the Invention
The present invention relates in general to a differential for a wheeled motor vehicle, which transmits a driving force from a prime mover, such as, engine, electric motor or the like to drive road wheels of the vehicle. More specifically, the present invention relates to a differential with an improved case (viz., differential case).
2. Description of the Related Art
For improving running performance and fuel consumption of motor vehicles, weight-reduction of the vehicles has been hitherto attempted in various ways. One of them is to reduce the weight of a differential, which is disclosed in, for example, Japanese Laid-open Patent Application (Tokkai) 2000-266162. In the way of this publication, a differential case for the differential is produced through a forging technique not by a casting technique that has been conventionally used. Due the nature of the forging, mechanical strength) of the differential case is increased and thus a so-called thin-walled structure can be provided for the differential case.
Usually, a differential is installed in a carrier case equipped with a lubricating oil pan, and a lower portion of the differential case is immersed in the lubricating oil in the pan. The lower portion of the case is formed with an oil inlet opening. That is, when the differential revolves, the lubricating oil in the pan is led into an interior of the differential case through the oil inlet opening thereby lubricating differential gears installed in the case.
As is known, for keeping the mechanical strength of the differential case at a satisfied level, the size of the oil inlet opening can not be made so large. However, if the opening is too small in size, the amount of the lubricating oil fed to the differential gears is reduced. Furthermore, thinning the wall of the differential case induces reduction in the length between a rotation axis of the case and the apertured lower portion of the case (viz., the outer diameter of the case), which would bring about an insufficient immersion of the oil inlet opening into the lubricating oil in the oil pan. Of course, in this case, the oil feeding to the differential gears becomes poor.